what happens to a 3/8" return line to the tank when it's funneled through a 1/4" tube through the sending unit ?
is it enough to worry about if the sending unit return is returned to 3/8" inside the tank ?
this is approximately 2" in length.
i'm thinking i should just replace the 1/4" with a piece of 3/8 and be done with it.
what say you guys ?
TIA as always !

IMO, any restriction in the fuel system is a restriction. Even in the return system. I replaced my 1/4” with 1/2” to match supply.

1/4 will not work

Even a 2" section is going to reduce volume to that of a 1/4" line.

If you want to get the full benefit of the larger line the whole run needs to be that size.

You tell us. Are you having an issue or not? A 1/4 inch return line will work just fine if you aren't trying to shove a ton of gas thru it. If your pump is matched to your engine then the return line shouldn't be flowing a huge amount of fuel. If the car is running now then put a pressure gauge on the return line to see if you have an issue.

andy, there is no issue now because this sender [and new stainless tank] is [are] not installed.
i am aware this is a possible restriction, and i'm pretty sure i will just change it to a 3/8 or 1/2" size. i've done that several times in the past, so it's no big deal.
i was wondering just "how much" of a restriction this "could" be.
an in tank electric pump will be used. [i haven't got that far yet] i will be starting with a carb, so i'll have to regulate the flow for that, but plans include going to FI some time in the future.
my car already has a 3/8" feed line, but still needs a return.
at that time, prepare for a bunch more questions from this old fart.
thanks for the replies so far guys !

I think you'll find that with too large a restriction in the return line, you won't be able to reduce the pressure in the line to the carb to a normal pressure (around 6-7 psi). When there's too much restriction in the return line, it builds up backpressure in the return line and the pressure regulator can't be adjusted low enough for the carburetor.

It is going to depend on the regulator pressure and the flows and pressures it will see (ie the the pump).

We took a look at a couple different regulators, and then more important for your question the effect of control pressures and flow rates in this thread.
https://www.forabodiesonly.com/mopa...b-stumble.437541/page-20#post-1972623639

very interesting article ! Thank You !

the diagrams give some insight and something to consider.
rigging up a test device of some sort to see what the 3/8 to 1/4 reduction would do, could give me an answer.
i'll have to do a little studying and see what i have laying around in the "plumbing" department.

it will ALL depend on the pump volume & pressure setting you want, a lower pressure will need a larger return with a high volume pump

Something I've run across: Are we talking line OD or ID ?

I was going to use hard line which is 3/8" OD but only 5/16" ID with a Carter 4601-HP electric pump. This is for
both the supply line and the return line (bypass-type regulator).

I know the rubber hose is 3/8" ID to fit over the brass fittings, but I don't want to use long lengths of rubber hose.

I have two factory type 3/8 supply lines, one for supply & one for return , the 255lph EFI pumpI was running worked great @ 6psi return set up for a carb, but not enough volume for my EFI set up, so I replace the intank pump with a 470 gph pump & it works great from 30psi &up. but any lower pressure with the large pump does not work.

Isn't the ideal solution to just plumb the regulator at tank on the return line, and just plumb the next size up short return then the supply iine?

that is another way of doing it, I WONT do it that way, I do what works for me , underhood temps cause lots of fuel delivery problems, the fuel never gets a chance to boil with the return up front, although I do have to insulate all the plumming

Not sure how I can understand how fuel is "boiling", under pressure and flowing, in that at low demand, most of fuel flows back to tank, and at high demand , it flows into engine.
How does it have time to boil?

When discussing tubing, nominal size is the actual o.d. (exception being in the plumbing trade where copper tubing nominal size is not o.d.)
Hose sizes typically are i.d.
So a 3/8 hose will slip over a 3/8 tube.

LOL Thats my point, regulator in the rear like you said, fuel is not moving under low demand in the engine compartment. like I said, I will do & recommend what has worked for me, you can do it the way you want.

We have a failure to communicate.

I think you are correct, it has been said by some manufacturers that the return regulator should be close to the carb or efi fuel rails for a more accurate pressure ?